The present invention relates to spectrum analysis, and more particularly to an instrumentation receiver for multichannel simultaneous realtime spectrum analysis with an offset frequency trigger to allow new measurements and new views of signals in the frequency domain.
Realtime spectrum analyzers, such as the Tektronix WCA300 and WCA200 instruments, offer the ability to trigger a spectrum acquisition based on the occurrence of an event in the frequency domain. See U.S. Pat. No. 5,103,402 together with FIG. 1 herein. Providing this frequency triggering function for a wideband intermediate frequency (IF) channel presents problems with implementation. The IF signal is digitized, windowed and transformed into the frequency domain typically by a fast Fourier transform (FFT). The resulting frequency domain data is compared in a frequency domain comparator stage with a user defined frequency domain mask to produce a trigger for a receiver acquisition system. The usefulness of the trigger function is based on its ability to trigger in real time. With the wideband IF channel being sampled at a very high rate, only a custom application specific integrated circuit (ASIC) would be able to provide the speed needed to perform the realtime triggering function for the wideband IF channel. Also since the wideband IF channel has reduced resolution, i.e., the number of bits provided by the analog-to-digital conversion (ADC) function, the amount of dynamic range for the frequency trigger function is limited. For some users high dynamic range is an important part of the frequency triggering function.
What is desired is a realtime instrumentation receiver that performs a triggering function on a spectral event in real time while providing high dynamic range.